The present invention relates to a composition for texturing a magnetic disk for providing the magnetic disk with texture grooves, and more particularly to a texturing composition for providing a surface of the magnetic disk with uniform texture grooves.
Remarkable advancement has recently been achieved for various computers including personal computers, accompanied by wide use of hard disk drives as external memory devices. The hard disk drive comprises one or more magnetic disks rotatable at a high speed and a magnetic head slightly floating on a surface of each magnetic disk for reading and writing digital signals. The magnetic disk generally has a layer structure comprising a substrate made of aluminum, etc., a primer layer made of Ni--P plating, etc., a magnetic layer formed by a coating method, a vapor deposition method, a sputtering method, etc., and a protective layer made of carbon, etc.
To meet the demand of memory density which is recently more and more increasing, a magnetic head is positioned closer to a surface of the magnetic disk, for instance, at a distance of about 0.1-3 .mu.m. Accordingly, the magnetic disk should have as flat a surface as possible, but the flattening of the magnetic disk surface increases a likelihood of a magnetic head sticking to the magnetic disk surface, thereby causing a trouble that the hard disk drive cannot be started.
To prevent the sticking of the magnetic disk to the magnetic disk surface, a primer layer lying beneath a magnetic layer in the magnetic disk is usually subjected to a texturing treatment. The texturing treatment comprises slidably pressing a grinding tape having abrasives of proper sizes attached to a surface thereof or a suspension of abrasives onto a surface of the primer layer of the magnetic disk in order to form fine texture grooves on the primer layer surface. In this case, it is necessary that the texture grooves are large enough to prevent the sticking of the magnetic head and small enough to prevent collision against the flying magnetic head. Further, the texture grooves should sufficiently be uniform.
Conventionally used as texturing compositions for forming such texture grooves are slurries comprising single-crystalline diamond abrasives obtained by high-pressure synthesis or single-crystalline fused alumina abrasives and grinding fluids which are water-soluble or insoluble grinding agents diluted with water. However, the single-crystalline diamond abrasives are expensive. Also, only a low texturing treatment speed is achieved with the single-crystalline alumina abrasives, and even when roughness of the textured surface is reduced, uneven texture grooves are obtained with a lot of scratches and burrs on the textured surface. The term "scratches" means linear deep grooves formed on the surface, much larger in width and depth than other texture grooves. The scratches are defined herein as grooves twice or more as large as other texture grooves in width or depth. The term "burrs" means projections remaining on the surface after abrasion with fine abrasives, and they are defined herein as projections of 1 .mu.m or more in length and 0.1 .mu.m or more in height.
Since the alumina abrasives are softer than the diamond abrasives, the alumina abrasives are so rounded to have fewer edge portions when pulverized that they less bite into an abraded surface than the diamond particles. As a result, the alumina abrasives are forced to scratch the textured surface. With such uneven texture grooves or burrs, a magnetic head moving relative to the magnetic disk while floating (flying) thereon is subjected to disturbed stress, resulting in deteriorated contact-start-stop (CSS) characteristics or crashing of the magnetic head to the magnetic disk surface which causes memory errors.
To further increase the memory density, it is necessary to reduce the surface roughness of the texturing primer layer of the magnetic disk, thereby decreasing a floating height of the magnetic head. However, if the single-crystalline diamond abrasives and the single-crystalline alumina abrasives are made small to have an average particle size of 1 .mu.m or less, these abrasives lose their edges to have rounded shapes, resulting in extreme decrease in cuttability. As a result, the abrasives tend to slide on the disk surface being textured without fully biting into the disk, failing to obtain uniform texture grooves.